1. Field of the Invention
The present invention pertains to medical equipment, and more particularly, to a therapeutic ultrasound system and methods used therewith for ablating obstructions within tubular anatomical structures such as blood vessels.
2. Description of the Prior Art
A number of ultrasound systems and devices have heretofore been proposed for use in ablating or removing obstructive material from blood vessels. Ultrasound catheters have been utilized to ablate various types of obstructions from blood vessels of humans and animals. Successful applications of ultrasound energy to smaller blood vessels, such as the coronary arteries, requires the use of relatively small diameter ultrasound catheters which are sufficiently small and flexible to undergo transluminal advancement through the tortuous vasculature of the aortic arch and coronary tree. However, all of these systems and devices generally encounter some problems.
A first type of problem relates generally to the effective transmission of ultrasound energy from an ultrasound source to the distal tip of the device where the ultrasound energy is applied to ablate or remove obstructive material. Since the ultrasound source, such as a transducer, is usually located outside the human body, it is necessary to deliver the ultrasound energy over a long distance, such as about 150 cm, along an ultrasound transmission wire from the source to the distal tip. Attenuation of the acoustical energy along the length of the transmission wire means that the energy reaching the distal tip is reduced. To ensure that sufficient energy reaches the distal tip, a greater amount of energy must be delivered along the transmission wire from the source to the distal tip. This transmission of increased energy along the transmission wire may increase the fatigue experienced by the transmission wire at certain critical locations, such as at the connection between the transducer and the transmission wire.
A second type of problem relates to the breakage of the ultrasound transmission member which extends through such catheters. Because of its small diameter, the ultrasound transmission member is particularly susceptible to breakage. Breakage of an ultrasound transmission member typically occurs near the proximal end thereof, generally within a few ultrasound nodes of the interface of the ultrasound catheter coupling and the ultrasound transducer coupling. This is believed to be because energy concentrations are highest at these points. In addition, significant amounts of heat can build up along the length of the ultrasound transmission member, and excessive heat can damage the integrity of the ultrasound transmission member.
A third type of problem relates to the need for accurately positioning the ultrasound device inside a patient's vasculature, and in particular, where the vasculature contains smaller and more tortuous vessels. To address this need, flexible and low-profile ultrasound devices have been provided which allow the device to be navigated through small and tortuous vessels. However, these devices have not been completely satisfactory in meeting these navigational needs.
A fourth type of problem relates to the actual ablation of the obstructive material. During the ultrasound procedure, the distal tip of the catheter is displaced to ablate the obstructive material. In this regard, it is desirable to have this displacement of the distal tip be operating in an optimum manner.
A fifth type of problem relates to the removal of particles that are produced when the obstructive material is ablated or broken up. It is important that these particles be removed from the patient's vascular system to avoid distal embolization and other clinical complications.
Thus, there still exists a need for improved ultrasound systems having ultrasound devices or catheters which address the aforementioned problems.